JP2014186905A - Fuel cell stack - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fuel cell stack indicating excellent startup and power generation performances.SOLUTION: A fuel cell stack 10 is configured by laminating a plurality of unit cells 12 each including an electrolytic film/electrode structure 34 interposing porous layers 56 and 62 between electrode catalyst layers 52 and 58 of a pair of electrodes 48 and 50 and gas diffusion layers 54 and 60. For a terminal unit cell 12a disposed in at least one end portion in a direction of lamination, percolation pressure of overlap bodies 64 and 68 of the gas diffusion layers 54 and 60 and the porous layers 56 and 62 is set higher than that of another unit cell 12b. The percolation pressure of the overlap bodies 64 and 68 in the terminal unit cell 12a is 30.0 to 125.0 kPa and the percolation pressure of the overlap bodies 64 and 68 in the other unit cell 12b is 10.0 to 125.0 kPa.

Description

  The present invention includes an electrode having an electrode catalyst layer and a gas diffusion layer on each side of a solid polymer electrolyte membrane, and at least one of the electrodes includes a porous layer between the electrode catalyst layer and the gas diffusion layer. The present invention relates to a fuel cell stack configured by laminating a plurality of unit cells each having an electrolyte membrane / electrode structure intervening.

  In recent years, various types of fuel cells have been developed. For example, it is known to use a polymer electrolyte fuel cell that operates at about 70 to 100 ° C. for in-vehicle applications. This polymer electrolyte fuel cell is usually used as a fuel cell stack in which a predetermined number of unit cells are stacked and end plates are provided at both ends in the stacking direction in order to obtain a desired power generation.

  In such a fuel cell stack, when starting from a stopped state, for example, warming is performed by self-heating by a power generation reaction, and the temperature is raised to an operating temperature. However, the end unit cells arranged at both ends in the stacking direction of the fuel cell stack are likely to dissipate heat to the outside of the fuel cell stack via the end plate or the like, and thus are arranged at the center in the stacking direction. It is difficult for the temperature to rise compared to other unit cells. Eventually, the heat from the end unit cell makes it difficult for the temperature of the entire fuel cell stack to rise, and the warm-up time may become longer.

  That is, there is a concern that the time required for obtaining a good power generation reaction after starting the fuel cell stack becomes long, and the starting performance of the fuel cell stack cannot be sufficiently obtained. In particular, when the fuel cell stack is used in a vehicle or the like, it is assumed that the fuel cell stack starts in a cold environment below freezing point. In this case, if the warm-up time becomes long as described above, it is particularly difficult to raise the temperature inside the end unit cell. In this case, the accumulated water is likely to freeze, and there is a concern that starting of the fuel cell stack becomes more difficult.

  Therefore, for example, in Patent Document 1, in the warm-up operation from when the fuel cell stack is started to when the operating temperature is reached, the temperature increase of the end unit cell is promoted to improve the low temperature startability of the fuel cell stack. It has been proposed. Specifically, in this fuel cell stack, the calorific value at the time of power generation in the end unit cells is made larger than in other unit cells.

JP 2006-196220 A

  As described above, the fuel cell stack described in Patent Document 1 focuses only on increasing the heat generation amount of the end unit cell of the fuel cell stack, and improves the power generation performance of unit cells other than the end unit cell. No consideration is given to making it happen. However, if the power generation reaction does not occur well in the unit cells other than the end unit cells, the heating of the fuel cell stack by the power generation reaction is not promoted, and it is difficult to sufficiently shorten the warm-up time. There is also a concern that good power generation performance cannot be obtained even in normal operation after the fuel cell stack reaches the operating temperature.

  The present invention solves this type of problem, and each of the end unit cell and other unit cells has appropriate characteristics, so that the temperature rise time of the end unit cell can be shortened, and the others An object of the present invention is to provide a fuel cell stack that can improve the power generation performance of each unit cell, and as a result, exhibits excellent starting performance and power generation performance.

To achieve the above object, the present invention provides an electrolyte membrane / electrode structure in which an electrolyte membrane made of a solid polymer membrane is sandwiched between an anode electrode and a cathode electrode, and the electrolyte membrane / electrode structure A fuel cell stack configured by stacking a plurality of unit cells having separators disposed on both sides,
Each of the anode electrode and the cathode electrode has an electrode catalyst layer facing the electrolyte membrane, and a gas diffusion layer,
At least one of the anode electrode or the cathode electrode further has a porous layer interposed between the electrode catalyst layer and the gas diffusion layer,
Of the plurality of unit cells, an end unit cell disposed at at least one end in the stacking direction overlaps the porous layer and the gas diffusion layer in comparison with other unit cells. The water permeability of the body is large,
And the hydraulic pressure of the said superimposition body of the said edge unit cell is 30.0-125.0kPa, The hydraulic pressure of the said superimposition body of the said other unit cell is 10.0-125.0kPa, It is characterized by the above-mentioned. To do.

  In the fuel cell stack according to the present invention, a porous layer is interposed between the electrode catalyst layer and the gas diffusion layer of each unit cell constituting the fuel cell stack. And about the water permeation pressure of the superposition body which piled up this porous layer and the gas diffusion layer, while setting the end unit cell larger, the numerical range in each of the end unit cell and other unit cells Set in the street. Thereby, in the warm-up operation from when the fuel cell stack is started until the operating temperature is reached, the temperature raising time of the end unit cell can be shortened. In addition, the power generation reaction of other unit cells can be favorably promoted in the warm-up operation and the subsequent normal operation.

  Specifically, since the end unit cell has a higher water permeation pressure than other unit cells, the supply of water and water vapor to the electrolyte membrane is suppressed, and the electrolyte membrane becomes relatively dry. As a result, the proton conductivity of the electrolyte membrane is reduced, the internal resistance is increased, and the heat generation amount is increased. That is, in the warm-up operation, the temperature raising time of the end unit cell can be shortened, and eventually the temperature raising time of the entire unit cell can be shortened.

  In addition, the other unit cell includes a porous layer, and the hydraulic pressure of the superposed body including the porous layer is set as described above, thereby maintaining the electrolyte membrane in a wet state during power generation. Excess water can be discharged effectively. As a result, it is possible to develop good proton conductivity in the electrolyte membrane and improve the diffusibility of the reaction gas, and the power generation reaction in other unit cells can be effectively promoted. As a result, the temperature raising time of the fuel cell stack in the warm-up operation can be shortened, and good power generation performance can be obtained even in the normal operation after the fuel cell stack reaches the operating temperature.

  Therefore, in this fuel cell stack, both the starting performance and the power generation performance can be effectively improved.

  Here, the number of unit cells constituting the fuel cell stack is typically 10 or more, and more preferably 20 or more, particularly when the fuel cell stack is for in-vehicle use. Further, the end unit cell is not limited to one unit cell provided at each end (endmost part) on both sides in the stacking direction of the fuel cell stack. 1 to 20% of the total number of stacked unit cells can be an end unit cell. For example, when the number of stacked unit cells is 20, unit cells from the endmost part to the fourth part (total of 8 at both ends) are set as end unit cells, and the remaining 12 units are other units. You may make it be a cell. Of course, the number of end unit cells at each end can be 1 to 3 (2 to 6 at both ends). Further, the end unit cell may be disposed only on one end side in the stacking direction of the fuel cell stack.

In the above fuel cell stack, the end unit cell has a lower water vapor discharge rate of the superimposed body than the other unit cell,
In addition, the water vapor discharge rate of the superposed body of the end unit cell is 14.0 to 18.0 mg / cm ² · min, and the water vapor discharge speed of the superposed body of the other unit cell is 18.0 to 20. It is preferably 0 mg / cm ² · min. In this case, shortening of the temperature rise time of the end unit cell and promotion of power generation reaction of other unit cells can be further effectively achieved, and both the starting performance and power generation performance of the fuel cell stack are more effective. Can be improved.

  According to the present invention, by appropriately setting each value of the end unit cell and the other unit cell for the water permeation pressure of the superposed body in which the porous layer and the gas diffusion layer are superimposed, the end portion in the warm air operation is set. The temperature raising time of the unit cell can be shortened, and the power generation performance of other unit cells can be improved satisfactorily. As a result, a fuel cell stack exhibiting excellent starting performance and power generation performance can be provided.

It is a perspective explanatory view of the fuel cell stack concerning the embodiment of the present invention. FIG. 2 is a schematic vertical sectional view of a main part of the fuel cell stack shown in FIG. 1. It is explanatory drawing which shows schematic structure of the control system which switches the edge part unit cell and center part unit cell of the fuel cell stack shown in FIG. 1, and connects to a load. It is a graph which shows the preparation conditions of a porous layer, and the physical-property value of a superimposition about unit cell A1-A3 for measurement samples, and B1-B3. It is a schematic block diagram of the measuring apparatus which measures the water vapor | steam discharge speed | rate of a superimposition body. It is a graph which shows the average voltage of a center part unit cell, and the temperature increase time of an end unit cell about the fuel cell stack of Examples 1-4 and Comparative Examples 1-4.

  Hereinafter, preferred embodiments of a fuel cell stack according to the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 is a perspective explanatory view of the fuel cell stack 10, and FIG. 2 is a schematic vertical sectional view of a main part of the fuel cell stack 10.

  In the fuel cell stack 10, a plurality of unit cells 12 are stacked in the direction of arrow A, and end plates 18, 18 are interposed at both ends in the stacking direction via terminal plates 14, 14 and insulating plates 16, 16. Is arranged (see FIG. 2).

  Also, as shown in FIG. 1, an oxidant gas inlet for supplying an oxidant gas such as an oxygen-containing gas to one end edge of the fuel cell stack 10 in the direction of arrow B and communicating with each other in the direction of arrow A A communication hole 20, a cooling medium inlet communication hole 22 for supplying a cooling medium such as pure water or ethylene glycol, and a fuel gas outlet communication hole 24 for discharging a fuel gas such as a hydrogen-containing gas are provided.

  In addition, the other end edge of the fuel cell stack 10 in the direction of arrow B communicates with each other in the direction of arrow A, a fuel gas inlet communication hole 26 for supplying fuel gas, and an oxidation for discharging oxidant gas. An agent gas outlet communication hole 30 and a cooling medium outlet communication hole 28 for discharging the cooling medium are provided.

  The end plates 18, 18 are fastened in the stacking direction by a plurality of tie rods 32, for example. The end plate 18 disposed on the distal end side of the tie rod 32 is formed with a screw hole (not shown) that is screwed with the male screw of the tie rod 32. Alternatively, a through hole may be formed in the end plate 18 instead of the screw hole, and a nut (not shown) may be screwed onto the tip of the tie rod 32.

  Further, a clamping load may be applied by adjusting a distance between the end plates 18 and 18 by interposing a plate (not shown) between the end plates 18 and 18. Further, a load may be applied between the end plate 18 and the insulating plate 16 with a disc spring (not shown) interposed therebetween.

  As shown in FIG. 2, each unit cell 12 is configured by stacking an electrolyte membrane / electrode structure 34, an anode side separator 36, and a cathode side separator 38 in a standing posture, for example. As the anode side separator 36 and the cathode side separator 38, for example, a carbon separator is used, but a metal separator may be used instead.

  A fuel gas passage 40 communicating with the fuel gas inlet communication hole 26 and the fuel gas outlet communication hole 24 is provided in a horizontal direction (arrow B direction) on the surface of the anode separator 36 facing the electrolyte membrane / electrode structure 34. It is provided to extend.

  Similarly, an oxidant gas passage 42 communicating with the oxidant gas inlet communication hole 20 and the oxidant gas outlet communication hole 30 is horizontally provided on the surface facing the electrolyte membrane / electrode structure 34 of the cathode side separator 38. It is provided to extend.

  Cooling that communicates with the cooling medium inlet communication hole 22 and the cooling medium outlet communication hole 28 between the surfaces of the anode side separator 36 and the cathode side separator 38 that face each other when a plurality of unit cells 12 are stacked. A medium flow path 44 is integrally formed.

  The electrolyte membrane / electrode structure 34 includes an electrolyte membrane 46 made of a solid polymer membrane, and an anode electrode 48 and a cathode electrode 50 that sandwich the electrolyte membrane 46. The outer dimension (surface area) of the electrolyte membrane 46 is set larger than the outer dimensions of the anode electrode 48 and the cathode electrode 50. As a result, the reaction gas supplied to one of the anode electrode 48 and the cathode electrode 50 passes through the electrolyte membrane 46 and moves to the other electrode, or from the electrolyte membrane / electrode structure 34 to the outside. Can be prevented from leaking (outleak).

  As the electrolyte membrane 46, for example, a film formed of a polymer that belongs to a cation exchange resin and has proton conductivity can be used. Examples of the cation exchange resin include sulfonated products of vinyl polymers such as polystyrene sulfonic acid, heat-resistant polymers such as perfluoroalkyl sulfonic acid polymer, perfluoroalkyl carboxylic acid polymer, polybenzimidazole, and polyether ether ketone. Examples thereof include a polymer having a sulfonic acid group or a phosphoric acid group introduced therein, a rigid polyphenylene obtained by polymerizing an aromatic compound having a phenylene chain as a main component, and a polymer having a sulfonic acid group introduced thereto.

  The anode electrode 48 includes a first electrode catalyst layer 52, a first gas diffusion layer 54, and a first porous layer 56. On the other hand, the cathode electrode 50 includes a second electrode catalyst layer 58, a second gas diffusion layer 60, and a second porous layer 62.

  The first electrode catalyst layer 52 includes carbon particles (catalyst particles) carrying a catalyst metal. As the carbon particles, carbon black can be used. In addition to this, for example, graphite, carbon fiber, activated carbon and the like, pulverized products thereof, and carbon compounds such as carbon nanofiber and carbon nanotube can be adopted. . On the other hand, as a catalyst metal, metals such as platinum, ruthenium, iridium, rhodium, palladium, osnium, tungsten, lead, iron, chromium, cobalt, nickel, manganese, vanadium, molybdenum, gallium, and aluminum are used alone or in combination. Can be used in combination.

  The first electrode catalyst layer 52 is provided so as to be joined to the electrolyte membrane 46, and the outer dimension is set smaller than that of the electrolyte membrane 46.

  The first gas diffusion layer 54 is made of, for example, carbon paper formed by containing a large number of fibrous carbons in cellulosic material. For example, a water-repellent resin made of FEP (tetrafluoroethylene / hexafluoropropylene copolymer) or the like may be contained in the base material. The outer dimension of the first gas diffusion layer 54 is set larger than that of the first electrode catalyst layer 52.

  The first porous layer 56 is a porous layer containing an electron conductive substance and a water repellent resin, and exhibits conductivity based on the electron conductive substance. Suitable examples of the electron conductive material include furnace black (“Ketjen Black EC” and “Ketjen Black ECP600JD” manufactured by Ketjen Black International, “Vulcan XC-72” manufactured by Cabot, and Tokai Carbon Co., Ltd. “Toka Black”, “Asahi AX” manufactured by Asahi Carbon Co., Ltd .; all trade names), acetylene black (“Denka Black” produced by Denki Kagaku Kogyo Co., Ltd .; trade names), crushed products of glassy carbon, vapor grown carbon fiber ("VGCF" and "VGCF-H" manufactured by Showa Denko KK; both are trade names), carbon nanotubes, and powders obtained by graphitizing them, or a mixture of two or more thereof.

  One water-repellent resin material is ETFE (tetrafluoroethylene / ethylene copolymer), PVDF (polyvinylidene fluoride), PVF (polyvinyl fluoride), ECTFE (chlorotrifluoroethylene / ethylene copolymer), PTFE. (Polytetrafluoroethylene), PFA (tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer), crystalline fluororesins such as FEP, “Lumiflon” and “Cytop” manufactured by Asahi Glass Co., Ltd. ) And the like, and silicone resins and the like can be exemplified, and these can be used alone or in combination of two or more.

  The outer dimension of the first porous layer 56 is set to be approximately equal to the outer dimension of the first gas diffusion layer 54, and the first porous layer 56 and the first gas diffusion layer 54 are overlapped to form a first superimposed body. 64 is configured.

  This first superposed body 64 has its water permeation pressure and water vapor discharge by appropriately adjusting the maximum pore diameter and thickness, the type and weight ratio of the electron conductive substance and the water repellent resin in the first porous layer 56, and the like. Speed can be set. Specific physical property values will be described later.

  As described above, the outer dimensions of the first electrode catalyst layer 52 are set smaller than those of the electrolyte membrane 46 and the first gas diffusion layer 54. For this reason, the outer peripheral edge of the electrolyte membrane 46 is exposed to the outside from the outer periphery of the first electrode catalyst layer 52, and the first porous layer 56 is between the exposed portion and the first gas diffusion layer 54. Intervenes. That is, the first porous layer 56 is interposed between the first electrode catalyst layer 52 and the first gas diffusion layer 54 and between the electrolyte membrane 46 and the first gas diffusion layer 54. As a result, the fibers constituting the first gas diffusion layer 54 can be prevented from piercing the electrolyte membrane 46 (particularly, the outer peripheral edge portion of the electrolyte membrane 46), and thus the physical deformation of the electrolyte membrane 46 can be suppressed.

  In addition, a frame-shaped first insulating sheet 66 is applied to the surface of the outer peripheral edge of the electrolyte membrane 46 that is exposed to the anode separator 36 from the outer periphery of the first superimposed body 64. It is provided to touch.

  The first insulating sheet 66 has gas impermeability, and is formed of, for example, a substantially flat film made of PEN (polyethylene naphthalate). In addition, since the thickness of the first insulating sheet 66 and the thickness of the first superimposed body 64 are substantially equal, the surfaces of the first insulating sheet 66 and the first superimposed body 64 (first gas diffusion layer 54) are flush with each other. In this state, it is in contact with the anode separator 36.

  Thus, by providing the 1st insulating sheet 66, it can avoid effectively that a reaction gas moves and mixes between the anode electrode 48 and the cathode electrode 50, and an out leak arises.

  The second electrode catalyst layer 58, the second gas diffusion layer 60, the second porous layer 62, the second superposed body 68 and the second insulating sheet 70 in the cathode electrode 50 are composed of the first electrode catalyst layer 52, the first gas described above. The diffusion layer 54, the first porous layer 56, the first superimposed body 64, and the first insulating sheet 66 are configured in the same manner. For this reason, the detailed description about the structure of the cathode electrode 50 is abbreviate | omitted. In the following description, when the first electrode catalyst layer 52 and the second electrode catalyst layer 58 are not particularly distinguished from each other, they are collectively referred to as an electrode catalyst layer. Similarly, the first gas diffusion layer 54 and the second gas diffusion layer 60 are the gas diffusion layer, and the first porous layer 56 and the second porous layer 62 are the same porous layer, the first superimposed body 64 and the second gas diffusion layer 60. Similarly, the superimposed body 68 is also referred to as a superimposed body.

  The anode side separator 36 and the cathode side separator 38 are provided with sealing members 72 and 72 so as to surround the edges of the first gas diffusion layer 54 and the second gas diffusion layer 60, respectively. Outleak can be effectively prevented by these seal members 72, 72.

  Next, a method for producing the above-described electrolyte membrane / electrode structure 34 will be described. In producing the electrolyte membrane / electrode structure 34, first, the electrolyte membrane 46 is produced in the shape of a rectangular sheet made of a polymer selected from the polymers belonging to the cation exchange resin and having proton conductivity.

  Then, the first electrode catalyst layer 52 is formed on one surface of the electrolyte membrane 46, and the second electrode catalyst layer 58 is formed on the other surface. Specifically, first, a catalyst paste is prepared by mixing the catalyst particles and an ionomer solution.

  Next, a predetermined amount of this catalyst paste is applied onto one surface of a film formed from PTFE or the like. Then, the surface of the film to which the catalyst paste is applied is thermocompression bonded to one surface of the electrolyte membrane 46. Thereafter, when the film is peeled off, the catalyst paste is transferred to one surface of the electrolyte membrane 46. Thereby, the first electrode catalyst layer 52 can be formed. Further, the second electrode catalyst layer 58 can be formed by transferring the catalyst paste to the other surface of the electrolyte membrane 46 in the same manner.

  Separately, the first porous layer 56 is formed on the first gas diffusion layer 54 to obtain the first superimposed body 64, and the second porous layer 62 is formed on the second gas diffusion layer 60. A second superimposed body 68 is obtained.

  Specifically, for example, the porous layer paste is prepared by mixing the electron conductive substance and the water repellent resin in an organic solvent such as ethanol, propanol, or ethylene glycol. And after apply | coating the predetermined amount of this paste for porous layers on the 1st gas diffusion layer 54, the 1st porous layer 56 is formed by heat-processing. Thereby, the first superimposed body 64 can be obtained.

  Similarly, after applying a predetermined amount of the porous layer paste on the second gas diffusion layer 60, the second porous layer 62 is formed by heat treatment. Thereby, the second superimposed body 68 can be obtained. In addition, the 1st superimposed body 64 and the 2nd superimposed body 68 may have a mutually different characteristic by being formed from the paste for porous layers adjusted so that it may mutually differ.

  Here, for example, the coating amount of the porous layer paste applied on the first gas diffusion layer 54 and the second gas diffusion layer 60, the electron conductive substance and the water repellent resin with respect to the organic solvent of the porous layer paste By adjusting the concentration (solid content concentration) and the like, the physical property values such as the water permeation pressure and the water vapor discharge rate of the first superimposed body 64 and the second superimposed body 68 can be adjusted. Furthermore, in order to adjust the physical property values of the first superimposing body 64 and the second superimposing body 68, the physical property values of the base materials constituting the first gas diffusion layer 54 and the second gas diffusion layer 60, the base material You may adjust the density | concentration etc. of the water-repellent resin impregnated in.

  Instead of the above production method, the first porous layer 56 and the second porous layer 62 may be obtained as a sheet-like molded body. In this case, by preparing the porous layer paste so that the concentration (solid content concentration) of the electron conductive material and the water-repellent resin with respect to the organic solvent is increased, the solvent is extracted and subjected to stretching treatment, etc. The 1st porous layer 56 and the 2nd porous layer 62 are formed as a sheet-like molded object.

  Then, the first porous layer 56 and the second porous layer 62 obtained as a sheet-like molded body are superimposed on each of the first gas diffusion layer 54 and the second gas diffusion layer 60. In this state, by applying pressure and heating (hot pressing), the first gas diffusion layer 54 and the first porous layer 56 can be thermocompression bonded to obtain the first superimposed body 64, and the second gas diffusion can be obtained. The second superposed body 68 can be obtained by thermocompression bonding the layer 60 and the second porous layer 62.

  The first superposed body 64 and the second superposed body 68 obtained as described above, the first porous layer 56 and the second porous layer 62 are respectively the first electrode catalyst layer 52 and the second electrode catalyst layer 58. Are integrated so as to face each other by thermocompression bonding. Thereby, the electrolyte membrane / electrode structure 34 is obtained.

  At this time, as described above, the porous layer is interposed between the gas diffusion layer and the electrode catalyst layer and between the gas diffusion layer and the electrolyte membrane 46. Thereby, even when a load due to thermocompression bonding is applied to the superposed body, it is possible to avoid the fibers of the gas diffusion layer from piercing the electrolyte membrane 46, and to suppress the physical deformation of the electrolyte membrane 46.

  The unit cell 12 is configured by sandwiching the electrolyte membrane / electrode structure 34 between the anode side separator 36 and the cathode side separator 38.

  Accordingly, the fuel cell stack 10 is configured by stacking, for example, 20 or more unit cells 12 configured as described above, and sandwiching both end portions between the end plates 18 and 18 as described above. The number of unit cells 12 to be stacked can be set so that a desired power generation can be obtained by the fuel cell stack 10. That is, when the fuel cell stack 10 is mounted on, for example, a fuel cell vehicle, the fuel cell stack 10 is configured by stacking a number of unit cells 12 that can generate electric power necessary for driving the vehicle. Can do.

  When the fuel cell stack 10 basically configured as described above is started from a stopped state, first, the fuel cell stack 10 is brought to an operating temperature (about 70 to 100 ° C.) by utilizing self-heating by a power generation reaction. Perform warm-up operation to raise the temperature. After the fuel cell stack 10 reaches the operating temperature, a normal operation for obtaining electric power by a power generation reaction is performed.

  Here, as shown in FIG. 2, among the plurality of unit cells 12, the end unit cells 12 a arranged at both ends in the stacking direction are connected to the end plate 18 via the terminal plate 14 and the insulating plate 16. In contact. For this reason, the end unit cell 12a is radiated to the outside of the fuel cell stack 10 through the end plate 18, and the other unit cells (center unit cell) 12b disposed in the center in the stacking direction There are many more. In the warm-up operation, if the amount of heat released from the end unit cell 12a is large and it is difficult to raise the temperature, the temperature raising time of the entire fuel cell stack 10 is prolonged. Therefore, in order to obtain good starting performance, it is necessary to shorten the temperature raising time of the end unit cell 12a and promote the power generation reaction of the central unit cell 12b during the warm-up operation.

  Therefore, in the fuel cell stack 10, the value of the end unit cell 12a is set to be larger than the value of the center unit cell 12b with respect to the hydraulic pressure of the superimposed body. Specifically, the hydraulic pressure of the superposed body of the end unit cell 12a is adjusted to 30.0 to 125.0 kPa, and the hydraulic pressure of the superposed body of the central unit cell 12b is adjusted to 10.0 to 125.0 kPa. It is carried out. These hydraulic pressures can be determined using, for example, a palm porometer manufactured by PMI (Porous Material, Inc). Needless to say, when the hydraulic pressure of the superposed body of the end unit cell 12a is 125.0 kPa, the hydraulic pressure of the superposed body of the central unit cell 12b is less than 125.0 kPa.

Further, in the fuel cell stack 10, the value of the end unit cell 12a is set to be smaller than the value of the center unit cell 12b with respect to the water vapor discharge speed of the superposed body. Specifically, the water vapor discharge rate of the superposed body of the end unit cell 12a is 14.0 to 18.0 mg / cm ² · min, and the water vapor discharge speed of the superposed body of the central unit cell 12b is 18.0 to 20 Adjustment is performed so as to be 0.0 mg / cm ² · min. These water vapor discharge rates can be determined using, for example, a measuring device 82 shown in FIG.

When the water vapor discharge rate of the central unit cell 12b is 18.0 mg / cm ² · min, the water vapor discharge rate of the end unit cell 12a is preferably less than 18.0 mg / cm ² · min.

  In the present embodiment, the physical property values of both the first superimposed body 64 and the second superimposed body 68 are set as described above, but at least one of the physical property values of the first superimposed body 64 and the second superimposed body 68 is set. May be set as described above.

  As described above, by setting the physical property values of the end unit cell 12a and the center unit cell 12b, respectively, the heat generation amount of the end unit cell 12a in the warming-up operation can be appropriately increased to promote the temperature rise. it can. Furthermore, the power generation reaction of the central unit cell 12b can be favorably promoted in the warm-up operation and the normal operation. That is, the starting performance and power generation performance of the fuel cell stack 10 can be preferably improved. Hereinafter, this effect will be described together with the operation of the fuel cell stack 10 with reference to FIGS. 1 to 3.

  When generating power in the fuel cell stack 10, the oxidant gas is supplied to the oxidant gas inlet communication hole 20 and the fuel gas is supplied to the fuel gas inlet communication hole 26. Further, the cooling medium is supplied to the cooling medium inlet communication hole 22.

  The cooling medium supplied to the cooling medium inlet communication hole 22 is introduced into a cooling medium flow path 44 formed between the anode side separator 36 and the cathode side separator 38. In the cooling medium flow path 44, the cooling medium moves in the direction of gravity (the direction of arrow C in FIG. 1). Therefore, the cooling medium is cooled over the entire power generation surface of the electrolyte membrane / electrode structure 34 and then discharged to the cooling medium outlet communication hole 28.

  The oxidant gas is introduced from the oxidant gas inlet communication hole 20 into the oxidant gas flow path 42 of the cathode side separator 38. The oxidant gas flows in the direction of arrow B along the oxidant gas flow path 42 and moves along the cathode electrode 50 of the electrolyte membrane / electrode structure 34.

  On the other hand, the fuel gas is introduced from the fuel gas inlet communication hole 26 into the fuel gas flow path 40 of the anode side separator 36. In the fuel gas channel 40, the fuel gas flows in the direction of arrow B, and moves along the anode electrode 48 of the electrolyte membrane / electrode structure 34.

  Therefore, in the electrolyte membrane / electrode structure 34, the fuel gas supplied to the anode electrode 48 and passed through the first gas diffusion layer 54 and the first porous layer 56, and supplied to the cathode electrode 50 and the second gas diffusion layer. 60 and the oxidant gas that has passed through the second porous layer 62 are consumed by the electrochemical reaction (electrode reaction) in the first electrode catalyst layer 52 and the second electrode catalyst layer 58, respectively, and electricity is generated.

More specifically, after the fuel gas supplied to the anode electrode 48 has passed through the first gas diffusion layer 54 and the first porous layer 56 via the fuel gas flow path 40, the hydrogen gas in the fuel gas is changed. The first electrode catalyst layer 52 is ionized to generate protons (H ⁺ ) and electrons. Electrons are taken out as electric energy for energizing a load 76 (see FIG. 3) electrically connected to the fuel cell stack 10, while protons are electrolyte membranes constituting the electrolyte membrane / electrode structure 34. The cathode electrode 50 is reached via 46. The proton moves from the anode electrode 48 side to the cathode electrode 50 side along with water contained in the electrolyte membrane 46.

  In the second electrode catalyst layer 58 of the cathode electrode 50, the protons, the electrons reaching the cathode electrode 50 after energizing an external load, and the second gas diffusion layer 60 and the second gas supplied to the cathode electrode 50 are supplied. The oxygen gas in the oxidant gas that has passed through the porous layer 62 is combined. As a result, water is generated. Hereinafter, this water is also referred to as generated water.

  In the electrolyte membrane / electrode structure 34, as described above, the first superposed body 64 is formed by interposing the first porous layer 56 between the electrolyte membrane 46 and the first gas diffusion layer 54, and the electrolyte membrane. A second superposed body 68 is formed by interposing a second porous layer 62 between 46 and the second gas diffusion layer 60. Due to the presence of the first porous layer 56 and the second porous layer 62, it is possible to appropriately achieve a balance between water retention and drainage in the anode electrode 48 and the cathode electrode 50 during the above electrode reaction.

  That is, in the present embodiment, the values of the water permeation pressure and the water vapor discharge rate of the superimposed body in the end unit cell 12a and the central unit cell 12b are set as described above. For this reason, in the end unit cell 12a, it becomes difficult for water vapor or the like to be supplied to the electrolyte membrane 46, and as a result of the electrolyte membrane 46 becoming relatively dry, the proton conductivity of the electrolyte membrane 46 slightly decreases. Along with this, the internal resistance increases, and the amount of heat generated during power generation of the fuel cell stack 10 increases.

  On the other hand, in the central unit cell 12b, the water vapor contained in the fuel gas in the anode electrode 48 and the generated water in the cathode electrode 50 excessively permeate the first porous layer 56 or the second porous layer 62. In addition, excessive damming is avoided. Therefore, water retention for maintaining the electrolyte membrane 46 in a wet state is sufficient, and drainage for diffusing the reaction gas quickly is also sufficient. For this reason, proton conduction easily proceeds in the electrolyte membrane 46, and the occurrence of flooding in the anode electrode 48 and the cathode electrode 50 is avoided, and the reaction gas diffuses easily. That is, good proton conductivity can be expressed in the electrolyte membrane 46, and the diffusibility of the reaction gas can be improved to promote the power generation reaction.

  The fuel cell stack 10 according to the present embodiment generates power as described above. However, in order to further improve the starting performance and power generation performance, the fuel cell stack 10 performs power generation under the control of the control system 74 shown in FIG. Also good. That is, the control unit 74 switches the unit cell 12 from which the current is taken out until the end unit cell 12a is heated to a predetermined temperature and after the end unit cell 12a has reached the predetermined temperature. Is preferred.

  Specifically, the fuel cell stack 10 has a terminal 75a for taking out current from all the unit cells 12 including the end unit cell 12a and a current from the unit cell 12 excluding the end unit cell 12a. Terminals 75b are provided on both ends in the stacking direction.

  The control system 74 selects one of the terminals 75a and 75b, and includes a changeover switch 78 connected to the load 76, a temperature sensor 80 for detecting the temperature of the end unit cell 12a, and a control unit (not shown). I have.

  When the temperature detected by the temperature sensor 80 is lower than 50 ° C., for example, the control unit controls the changeover switch 78 so that the terminal 75a and the load 76 are connected as shown in FIG. On the other hand, when the temperature detected by the temperature sensor 80 is, for example, 50 ° C. or higher, the changeover switch 78 is controlled so that the terminal 75b and the load 76 are connected as shown by the wavy line in FIG.

  Therefore, when the fuel cell stack 10 is started from a stopped state, the central unit cell 12b and the central unit cell 12b generate a larger amount of heat until the temperature of the end unit cell 12a reaches 50 ° C. A power generation reaction is caused in both of the end unit cells 12a. Thereby, the temperature of the fuel cell stack 10 can be effectively increased. That is, the temperature raising time of the fuel cell stack 10 in the warm-up operation can be shortened, and the starting performance can be improved satisfactorily.

  Then, after the temperature of the end unit cell 12a reaches 50 ° C., a current is taken out from the central unit cell 12b, which has higher power generation performance than the end unit cell 12a. Thereby, the power generation performance during normal operation can be improved more effectively.

  In addition, this invention is not specifically limited to above-described embodiment, A various deformation | transformation is possible in the range which does not deviate from the summary.

  For example, in the above embodiment, the electrolyte membrane / electrode structure 34 having the first porous layer 56 and the second porous layer 62 is illustrated, but the first porous layer 56 and the second porous layer 62 are illustrated. There is no need to provide both of them, and only one of them may be provided. In particular, it is preferable to provide the second porous layer 62 on the cathode electrode 50 side where water is generated by an electrode reaction.

  Further, in the above embodiment, the end unit cell 12 a is configured by one unit cell 12 disposed at the extreme end (endmost part) on both sides in the stacking direction of the fuel cell stack 10. However, it is not particularly limited to this. The number of end unit cells can be arbitrarily set between 1 to 20% of the total number of unit cells constituting the fuel cell stack. In this case, it is preferable that the end cells at both ends are adjacent (concentrated). Further, the end unit cell 12 a may be disposed only on one end side in the stacking direction of the fuel cell stack 10.

  As unit cells for measurement samples, unit cells A1 to A3 and B1 to B3 were prepared as follows based on the preparation conditions of the porous layer shown in FIG.

[Unit cell A1]
(1) The gas diffusion layer is a dispersion of tetrafluoroethylene-hexafluoropropylene copolymer (FEP) manufactured by Mitsui-DuPont Fluorochemical Co., Ltd. on carbon paper having a bulk density of 0.31 g / m ² and a thickness of 190 μm. The liquid “FEP 120-JRB Dispersion” (trade name) was impregnated and dried at 120 ° C. for 30 minutes to perform a water repellent treatment. At this time, the carbon paper was impregnated in the dispersion so that the dry weight of FEP with respect to the carbon paper was 2.4% by weight.

  (2) The porous layer paste includes 12 g of vapor growth carbon “VGCF” (trade name) manufactured by Showa Denko KK, and FEP dispersion (solid content concentration 54%) “FEP120JRB” manufactured by Mitsui / DuPont Fluorochemicals. ”(Trade name) and 20 g of ethylene glycol were prepared by stirring and mixing with a ball mill.

  (3) Screen printing was performed on the gas diffusion layer prepared in (1) above using the porous layer paste prepared in (2) as an ink so that the thickness of the porous layer was 7.4 μm. . And the porous layer was formed by performing the heat processing for 30 minutes at 380 degreeC, and the superimposed body was obtained.

  (4) The catalyst paste is such that the weight ratio of the platinum catalyst “LSA” (trade name) made by BASF is 0.1 with respect to the ion conductive polymer solution “DE2020CS” (trade name) made by DuPont. Further, it was prepared by stirring and mixing with a ball mill.

(5) After applying the catalyst paste prepared in (4) above on a PTFE sheet so that the weight of platinum is 0.4 mg / cm ² , heat treatment is performed at 120 ° C. for 60 minutes to obtain a cathode electrode A sheet for transferring the first electrode catalyst layer to one surface of the electrolyte membrane was prepared.

(6) A ^second anode electrode was prepared in the same manner as in (5) above except that the catalyst paste prepared in (4) above was applied on a PTFE sheet so that the weight of platinum was 0.1 mg / cm 2. A sheet for transferring the electrode catalyst layer to the other surface of the electrolyte membrane was prepared.

  (7) The catalyst paste application side of the sheet prepared in (5) above and the other side of the electrolyte membrane on one side of the fluorine-based electrolyte membrane having a thickness of 24 μm and an ion exchange capacity of 1.05 meq / g The PTFE sheet was peeled off after thermocompression bonding the catalyst paste application side of the sheet prepared in (6) to the surface. That is, the first electrode catalyst layer was formed on one surface of the electrolyte membrane and the second electrode catalyst layer was formed on the other surface by the decal method.

(8) On each electrode catalyst layer formed on the electrolyte membrane prepared in (7) above, the porous layer on the gas diffusion layer prepared in (3) above is 120 ° C. under a surface pressure of 15 kgf / cm ² . Thermocompression bonding was performed. By the above method, each of the anode electrode and the cathode electrode was produced in the same manner to obtain an electrolyte membrane / electrode structure.

  (9) Unit cell A1 was produced by sandwiching the electrolyte membrane / electrode structure produced in (7) above with a separator.

[Unit cell A2]
Instead of the step (3), the thickness of the porous layer is 22.3 μm on the gas diffusion layer prepared in (1) above, using the porous layer paste prepared in (2) as an ink. Screen printing was performed. Other than that was carried out similarly to unit cell A1, and obtained unit cell A2.

[Unit cell A3]
Instead of the step (3), the thickness of the porous layer is 55.2 μm on the gas diffusion layer prepared in (1) above, using the porous layer paste prepared in (2) as an ink. Screen printing was performed. Other than that was carried out similarly to unit cell A1, and obtained unit cell A3.

[Unit cell B1]
Instead of the step (3), the porous layer paste prepared in (2) above is applied onto the gas diffusion layer prepared in (1) so as to have a thickness of 14.3 μm. It applied using. Other than that was carried out similarly to unit cell A1, and obtained unit cell B1.

[Unit cell B2]
Instead of the step (3), the porous layer paste prepared in (2) above is applied to the gas diffusion layer prepared in (1) so as to have a thickness of 31.4 μm. It applied using. Other than that was carried out similarly to unit cell A1, and obtained unit cell B2.

[Unit cell B3]
Instead of the step (3), the porous layer paste prepared in (2) above is applied onto the gas diffusion layer prepared in (1) so as to have a thickness of 48.2 μm. It applied using. Other than that was carried out similarly to unit cell A1, and obtained unit cell B3.

With respect to the unit cells A1 to A3 and B1 to B3, the water permeation pressure [kPa] and the water vapor discharge rate [mg / cm ² · min] of either one of the anode electrode and the cathode electrode were determined. The results are shown in FIG. 4 together with the conditions for producing the porous layer.

  The water permeation pressure of the superimposed body was measured using a palm porometer manufactured by PMI (Porous Material, Inc). Specifically, first, the superimposed body is punched into a circular shape having a diameter of 1 inch to produce a measurement sample. On the porous layer of the measurement sample, pure water is dropped to form a water film, and air pressure is gradually applied to the water film by a palm porometer. Then, the water permeation pressure of the superimposed body is calculated by measuring the minimum pressure required for pure water to begin to permeate the measurement sample.

  The water vapor discharge speed of the superposed body was obtained using a measuring device 82 shown in FIG. The measuring device 82 includes an air supply unit 84 that supplies dry air, a sample storage container 88 that stores a measurement sample 86, and a water supply unit 90 that supplies pure water to the sample storage container 88. In the following description, dry air is also referred to as air and pure water is also referred to as water.

  The air supply unit 84 includes a cylinder 92 that stores air, and a supply pipe 94 provided from the cylinder 92 to the sample storage container 88. The supply pipe 94 is provided with a regulator 96 and a mass flow controller (MFC) 98 for adjusting the mass flow rate of air.

  The sample storage container 88 includes a storage tank 100 and a lid member 102 that closes the upper open end of the storage tank 100, and a water supply hole 104 is formed at the bottom of the storage tank 100 therein. The water supply unit 90 supplies water into the sample storage container 88 through the water supply hole 104.

  The stored water W is stored in the storage tank 100, and the punching metal 106, the nonwoven fabric 108, and the measurement sample 86 are stacked in this order above the stored water W.

  A plurality of through holes 110 are formed in the punching metal 106. Further, a measurement sample 86 is placed on the punching metal 106 via a nonwoven fabric 108. The measurement sample 86 is manufactured by punching the superposed body into a square shape having a side of 4.2 cm.

  The lid member 102 covers the upper end of the opening of the storage tank 100, and a flow path portion 112 is formed on the surface in contact with the measurement sample 86. The flow path part 112 imitates the fuel gas flow path 40 formed in the anode side separator 36 constituting the fuel cell stack 10 or the oxidant gas flow path 42 formed in the cathode side separator 38. The supply pipe 94 and the discharge pipe 114 are communicated with each other. The lid member 102 is heated by a heater (not shown) or the like, and the temperature is maintained at 70 ° C.

  The water supply unit 90 stores water and is connected to the water supply hole 104 of the storage tank 100 via the water supply pipe 116, the water level sensor 120 that detects the water level in the tank 118, and the detection of the water level sensor 120. Based on the result, a pump 122 for supplying water into the tank 118 from a pure water supply source (not shown) is provided to keep the water level in the tank 118 constant.

  In the measuring apparatus 82 configured as described above, first, the air stored in the cylinder 92 is supplied via the supply pipe 94. After the pressure is adjusted by passing through the regulator 96, the air is adjusted to a flow rate of 5 L / min by the MFC 98, and further, the temperature is adjusted to 70 ° C. by a heater or the like (not shown). It is supplied into the flow path part 112.

  As described above, the air at 70 ° C. is supplied to the flow path portion 112 and the temperature of the lid member 102 is maintained at 70 ° C., so that heat is transmitted to the stored water W in the storage tank 100. As a result, the stored water W evaporates and steam is generated. The generated water vapor rises through the through hole 110 of the punching metal 106, is diffused by the nonwoven fabric 108, and is then supplied to one surface of the measurement sample 86.

  The water vapor further passes through the measurement sample 86 along the film thickness direction, and is discharged from the other surface of the measurement sample 86 and then reaches the flow path portion 112. The water vapor that has reached the flow path portion 112 is discharged from the discharge pipe 114 to the outside of the sample storage container 88 together with the air supplied from the air supply portion 84.

  At this time, each time the stored water W passes through the pores of the measurement sample 86 as water vapor and is discharged to the outside, the same amount of water lost as water vapor is supplied from the tank 118 to the water supply pipe 116 and the water supply. It is supplied into the storage tank 100 through the hole 104. Corresponding to this supply, the water level in the tank 118 falls according to the rate at which water vapor is discharged from the measurement sample 86.

  When the water level in the tank 118 falls below a predetermined threshold preset in the water level sensor 120, the sequence control functions and the pump 122 is energized. As a result, new water is supplied into the tank 118. The amount of water supplied at this time is an amount corresponding to the amount of water vapor discharged from the measurement sample 86. Therefore, the water vapor discharge speed of the measurement sample 86 is calculated based on the supply amount and the time from the start of the supply of air to the start of the supply of water to the tank 118.

  One of the unit cells A1 to A3 produced as described above is selected as the end unit cell, and one of the unit cells B1 to B3 is selected as the center unit cell. Then, the unit cells selected as the end unit cells are stacked on both ends of the eight unit cells selected as the center unit cells, that is, the sum of the two end unit cells and the eight unit cell units. Ten fuel cells were stacked to produce fuel cell stacks of Examples 1 to 4. Further, any one of the unit cells A1 to A3 and B1 to B3 was selected, and the selected 10 unit cells were stacked to produce fuel cell stacks of Comparative Examples 1 to 4.

  That is, in the fuel cell stacks of Examples 1 to 4, the hydraulic pressure of the superposed body of the end unit cell is larger than that of the central unit cell, and the water vapor discharge rate of the superposed body of the end unit cell is the central unit. It is configured to be smaller than the cell. Moreover, in the fuel cell stacks of Comparative Examples 1 to 4, the end unit cell and the central unit cell are composed of similar unit cells. Specifically, as shown in FIG. 6, fuel cell stacks of Examples 1 to 4 and Comparative Examples 1 to 4 were obtained by selecting an end unit cell and a center unit cell, respectively.

  About these Examples 1-4 and Comparative Examples 1-4, the temperature increase required time (s) when an edge part unit cell rises from -10 degreeC to 0 degreeC, and the center part unit cell 100s after starting The average voltage (mV) was obtained and shown in FIG.

The operating conditions of the fuel cell stack when obtaining the measurement results shown in FIG. 6 are as follows: start temperature: −10 ° C., output current density: 0.5 A / cm ² , gas utilization rate: fuel gas 70% and oxidizer Gas pressure of gas 50%, fuel gas and oxidant gas; 100 kPaG.

4 and 6, it can be seen that in Examples 1 to 4, the time required for temperature increase in the end unit cells is shorter than that in Comparative Examples 1 to 4, and the average voltage of the center unit cell is large. In Examples 1 to 4, the water permeability of the superposed body of the end unit cells is in the range of 30.0 to 125.0 kPa, and the water vapor discharge rate is in the range of 14.0 to 18.0 mg / cm ² · min. The unit cell superposed body has a water permeability of 10.0 to 125.0 kPa and a water vapor discharge rate of 18.0 to 20.0 mg / cm ² · min. That is, by setting the water permeation pressure and water vapor discharge rate of the superposed body of each of the central unit cell and the end unit cell within the above ranges, the temperature rise time of the end unit cell can be shortened, The average voltage of the unit cell could be increased. That is, the starting performance and power generation performance of the fuel cell stack could be improved satisfactorily.

DESCRIPTION OF SYMBOLS 10 ... Fuel cell stack 12 ... Unit cell 12a ... End unit cell 12b ... Center unit cell 14 ... Terminal plate 16 ... Insulating plate 18 ... End plate 20 ... Oxidant gas inlet communication hole 22 ... Cooling medium inlet communication hole 24 ... Fuel gas outlet communication hole 26 ... Fuel gas inlet communication hole 28 ... Cooling medium outlet communication hole 30 ... Oxidant gas outlet communication hole 32 ... Tie rod 34 ... Electrolyte membrane / electrode structure 36 ... Anode side separator 38 ... Cathode side separator 40 ... Fuel gas flow path 42 ... Oxidant gas flow path 44 ... Cooling medium flow path 46 ... Electrolyte membrane 48 ... Anode electrode 50 ... Cathode electrode 52 ... First electrode catalyst layer 54 ... First gas diffusion layer 56 ... First porous layer 58 ... second electrode catalyst layer 60 ... second gas diffusion layer 62 ... second porous layer 64 ... first superposed body 66 ... first insulating sheet 68 ... second superposed body 70 ... 2nd insulating sheet 72 ... Seal member 74 ... Control system 82 ... Measuring device

Claims (2)

A unit cell having an electrolyte membrane / electrode structure in which an electrolyte membrane made of a solid polymer membrane is sandwiched between an anode electrode and a cathode electrode, and separators disposed on both sides of the electrolyte membrane / electrode structure. A fuel cell stack configured by stacking a plurality of fuel cells,
Each of the anode electrode and the cathode electrode has an electrode catalyst layer facing the electrolyte membrane, and a gas diffusion layer,
At least one of the anode electrode or the cathode electrode further has a porous layer interposed between the electrode catalyst layer and the gas diffusion layer,
Of the plurality of unit cells, an end unit cell disposed at at least one end in the stacking direction overlaps the porous layer and the gas diffusion layer in comparison with other unit cells. The water permeability of the body is large,
And the hydraulic pressure of the said superimposition body of the said edge unit cell is 30.0-125.0kPa, The hydraulic pressure of the said superimposition body of the said other unit cell is 10.0-125.0kPa, It is characterized by the above-mentioned. Fuel cell stack. The fuel cell stack according to claim 1, wherein the end unit cell has a lower water vapor discharge rate of the superimposed body than the other unit cell,
In addition, the water vapor discharge rate of the superposed body of the end unit cell is 14.0 to 18.0 mg / cm ² · min, and the water vapor discharge speed of the superposed body of the other unit cell is 18.0 to 20. A fuel cell stack characterized by being 0 mg / cm ² · min.

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